Semiconductor optical mask data preparation includes one or more processes that rely upon identifying features of interest in mask data. One such process may include, for example, placing marks at coordinates in mask data where a particular feature of interest needs to be measured. Given a description of a feature of interest, locations that fit the description may be found so that one or more marks may be placed on each such location. The marks can be translated into specially formatted metrology files used by optical tools or a critical dimension (CD) scanning electron microscope (SEM). For example, the marks may be used for in-process quality control in conjunction with one or more CDs to determine if a manufacturing process is correctly producing an IC. The term critical dimension refers to a size of a feature of a semiconductor that can be measured, in nanometers for example, that is related to the minimum feature size that can be created on that semiconductor wafer using a particular technology.